This invention is an improvement on the invention disclosed in our prior U.S. Pat. No. 5,009,564, issued Apr. 23, 1991. The disclosure of that prior patent is hereby incorporated herein by reference.
The invention disclosed in our prior patent and other devices of this general type suffered from a drawback which we will now explain with reference to FIGS. 1-5 and 21.
FIGS. 1-3 and 21 show the invention disclosed in our prior patent. A device of this character is designed to unload a load of generally solid, but discrete, matter 10 (such as garbage or sand) from a trailer 12. Unloading is effected in steps by the combined use of a movable floor 14 and a movable bulkhead 16. Unloading is begun by opening a rear door (not shown). Then the movable floor 14 and the movable bulkhead 16 move backwardly together by one increment under control of drive means not shown, thereby ejecting a first increment of the matter 10 as shown in FIG. 1. Since the movable floor 14 and the movable bulkhead 16 move together in the first step, there is relatively little tendency for the matter 10 to press outwardly against the sides of the trailer 12 or upwardly against the roof of the trailer 12. In the next step, however, the movable floor 14 is moved toward the front of the truck 12 while the movable bulkhead 16 is held in place. This causes the matter 10 to compact and to exert considerable upward pressure on the roof of the trailer 12 (as shown in FIG. 2) and considerable sideward pressure on the sides of the trailer 12 (as shown in FIG. 5 for the prior art). The upward and outward pressures can damage the trailer 12. FIG. 3 shows the next step of the cycle, during which the movable floor 14 and the movable bulkhead 16 again move backwardly together by one increment, ejecting a second increment of the matter 10.
FIGS. 4 and 5 show the prior art that preceded our previous invention. In this prior art, matter 18 (such as garbage or sand) is unloaded from a trailer 20 by means of a movable bulkhead 22, but there is no movable floor. Since the floor is stationary relative to the movable bulkhead 22, the matter 18 tends to compact and press upwardly on the roof of the trailer 20 (as shown in FIG. 4) and outwardly on the sides of the trailer 20 (as shown in FIG. 5) as the movable bulkhead 22 moves backwardly, thereby stressing and sometimes damaging the trailer 20.